We report the analysis of time-resolved spectroscopy of IP Pegasi in
outburst with eclipse mapping techniques to investigate the location
and geometry of the observed spiral structures. We were able to obtain
an improved view of the spiral structures with the aid of light curves
extracted in velocity bins matching the observed range of velocities
of the spiral arms combined with a double default map tailored for
reconstruction of asymmetric structures.
Two-armed spiral structures are clearly seen in all eclipse maps.
The arms are located at different distances from the disc centre.
The “blue” arm is farther out in the disc ()
than the “red” arm ().
There is evidence that the velocity of the emitting gas along the
spiral pattern is lower than the Keplerian velocity for the same disc
radius. The discrepancy is smaller in the outer arm (measured velocities
10–15 per cent lower than Keplerian) and is more significant in the
inner arm (observed velocities up to 40 per cent lower than Keplerian).
We measured the opening angle of the spirals from the azimuthal
intensity distribution of the eclipse maps to be .
A comparison with similar measurements on data at different outburst
stages reveals that the opening angle of the spiral arms in IP Peg
decreases while the outbursting accretion disc cools and shrinks,
in agreement with the expected evolution of a tidally driven spiral wave.
The sub-Keplerian velocities along the spiral pattern and the clear
correlation between the opening angle of the spirals and the outburst
stage favors the interpretation of these asymmetric structures
as tidally-induced spiral shocks.

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.